Final answer:
T cells become MHC restricted through a selection process in the thymus that ensures they can recognize peptides presented by self-MHC molecules without reacting to self-peptides, thus establishing self-tolerance. They are activated by specific antigens presented on MHC molecules leading to clonal expansion and immune response.
Step-by-step explanation:
How T Cells Become MHC Restricted
The concept of T cells becoming MHC restricted refers to the process by which T cells learn to recognize peptides presented by self-MHC molecules, a process central to the adaptive immune response. This happens during the T cell's development in the thymus, where they undergo a selection process to ensure they can recognize self-MHC, but not react against self-peptides, a state known as self-tolerance.
Mature T cells get activated upon recognition of a processed foreign antigen presented by self-MHC molecules, leading to clonal expansion necessary for a strong immune response. Clonal selection ensures that only T cells with receptors specific to that antigen are selected, meaning each activated T cell and its progeny recognizes a specific pathogen signature.
Naïve CD4+ T cells, for example, engage with MHC II molecules on antigen-presenting cells (APCs), becoming helper T cells that activate B cells and CD8+ T cells, the latter turning into cytotoxic T cells that can kill infected cells. CD8+ T cells, in contrast, become activated in response to antigens presented with MHC I molecules.